<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        div+p{
            color: red;
        }
        p:hover{
            color: #1abebf;
        }
        input:focus{
            background-color: red;
        }
        div:before{
            content: "我是前面";
            display: block;}

            div:after{
                content: "我是后面";
                display: block;

            }



    </style>
</head>
<body>
<div>我是div</div>

</body>
</html>